I've said nothing about what "deserves" preservation, but only what sort of things tend to be preserved over periods on the scale of centuries. And yes: My contention is that unless a substantial community of people voluntarily commit to preserving something, it likely will not survive (or will do so accidentally).

I'm not quite following why this is not relevant to the OP's question. I suppose I'm saying that it's not just a hard task, but an almost impossible one. Lots of people (2000 years ago, say) thought that what they were writing was of world-historical significance; today, we barely know their names. Others dashed off dictated letters to small, fragile communities of early followers and just happened to have created among the most well preserved texts of all time.

All I'm really saying here is that among the titanic forces determining which is which, the type of ink used seems not to be a matter of much importance.

It's a different side to the question that others are answering, and it's interesting to think about.

What does last? Making something a tradition can help smooth over logic. Making it part of a long running organisation would help (organisations can exist for multiple centuries).

Perhaps an organisation dedicated to preserving messages through the ages, and encourage - say - a Christmas message? More people involved mean more care.

I think those are orthogonal.

Sure, you have the biggest chance of having something preserved if enough people care about it. This is a case where, as you rightly point out, technology matters not.

But we can still discuss technologies of preservation, especially in the light of non-physical creations like works presented on a digital machine.

And the very fact it survives makes it noteworthy - if archeologists found a collection of well preserved shitposts from 2500 BC it would be valuable - even if worthless when recorded.